Polarizers included in polarizing plates are optical devices for polarizing natural light or arbitrarily polarized light in a particular direction, and are widely used in display devices such as liquid crystal displays (LCDs) or organic light emitting diode (OLED) displays. Currently, polyvinyl alcohol-based polarizing films, containing an iodine-based compound or a dichroic dye and having a molecular structure in which molecular chains are oriented in a particular direction, are generally used as polarizers of display devices.
As disclosed in many patent documents of the related art, polyvinyl alcohol-based polarizing films are commonly manufactured by dyeing a polyvinyl alcohol-based film with iodine or a dichroic dye, stretching the polyvinyl alcohol-based film in a particular direction, and performing a cross-linking process. In this case, the stretching process may be a wet stretching process using a solution such as an aqueous boric acid solution or an aqueous iodine solution, or a dry stretching process performed in the atmosphere.
The optical characteristics of a polarizing plate including such a polyvinyl alcohol-based polarizing film are predominantly affected by an iodine complex functioning as a dichroic dye, and it is important to increase the degree of orientation of a polyvinyl alcohol-iodine complex for improving optical characteristics of the polarizing plate. However, it may be difficult to improve the degree of orientation of such an iodine complex.
Furthermore, in the above-described manufacturing process of the related art, the thickness of a polyvinyl alcohol-based film has to be 60 μm or greater before stretching so as to prevent breakage of the polyvinyl alcohol-based film during stretching. In this case, however, there is a limit to reducing the thickness of a polarizer by stretching.
Therefore, there is a need for a new technique for manufacturing a thin polarizer having a thickness of 10 μm or less without failures such as breakages, while improving the optical characteristics of the thin polarizer by increasing the degree of orientation of a polyvinyl alcohol-iodine complex.